Taphonomic Aspects of Crowned Hawk-Eagle Predation on Monkeys
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Journal of Human Evolution 44 (2003) 87–105 Taphonomic Aspects of Crowned Hawk-Eagle Predation on Monkeys William J. Sandersa*, Josh Trapania,b, John C. Mitanic a Museum of Paleontology, University of Michigan, 1109 Geddes Avenue, Ann Arbor, MI 48109-1079, USA b Department of Geological Sciences, University of Michigan, 2534 C.C. Little Building, 425 E. University, Ann Arbor, MI 48109-1063, USA c Department of Anthropology, University of Michigan, 500 South State Street, Ann Arbor, MI 48109-1382, USA Received 24 January 2002; accepted 11 November 2002 Abstract This study provides a taphonomic analysis of prey accumulations of crowned hawk-eagles (Stephanoaetus coronatus) from Ngogo, Kibale National Park, Uganda, collected over 37 months from below nests of two eagle pairs. Crowned hawk-eagles are powerful predators capable of killing animals much larger than themselves, and are significant predators of cercopithecoid monkeys in forest habitats throughout sub-Saharan Africa. At Ngogo, 81% of the individuals in the kill sample are monkeys. Redtail monkeys (Cercopithecus ascanius) are particularly well represented in the sample, making up 66% of monkeys identified to species. Despite an impressive killing apparatus, crowned hawk-eagles are fastidious eaters that inflict far less damage to bone than mammalian predators. Examination of skeletal material from the Ngogo kill sample reveals that crania, hindlimb elements, and scapulae survive predation better than do other bones. Crania of adults are typically complete and accompanied by mandibles, while crania of young individuals are usually dissociated from mandibles and lack basicrania and faces. Long bones are often whole or show minimal damage. Thin bones, such as crania and innominates, are marked by numerous nicks, punctures, and “can-opener” perforations. Scapular blades are heavily raked and shattered. Along with the strong preference for cercopithecoids, these distinct patterns of bone survival and damage indicate the feasibility of recognizing specific taphonomic signatures of large raptors in fossil assemblages. Berger and Clarke (1995) hypothesized that crowned hawk-eagles or similar large raptors were principally responsible for the accumulation of the late Pliocene fossil fauna from Taung, South Africa, including the type infant skull of Australopithecus africanus. The results of our study suggest that the faunal composition and type of damage to the hominid skull and other bone from Taung are consistent with the predatory activities of large raptors. More rigorous assessment of their hypothesis will require sorting the Taung fauna by locality and further detailed analysis of species composition and bone damage and survivability patterns. 2003 Elsevier Science Ltd. All rights reserved. Keywords: Crowned hawk-eagle; Predation; Taphonomy; Cercopithecoid monkeys; Taung * Corresponding author. Tel.: +1-734-647-2098 E-mail addresses: [email protected] (W.J. Sanders), [email protected] (J. Trapani), [email protected] (J.C. Mitani). 0047-2484/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0047-2484(02)00196-3 88 W.J. Sanders et al. / Journal of Human Evolution 44 (2003) 87–105 Introduction Recently, crowned hawk-eagles were implicated as possible accumulators of the faunal assemblage Crowned hawk-eagles (Stephanoaetus corona- from the late Pliocene site of Taung, South Africa tus) are large (weight, 3.4–4.1 kg; length, 81– (Berger and Clarke, 1995), which includes cerco- 92 cm), immensely powerful raptors (Steyn, 1973; pithecoid bones and the infant type skull of Williams and Arlott, 1980; Brown et al., 1982). Australopithecus africanus (Cooke, 1990). Results Armed with deep, well-curved beaks, thick legs, of our analysis have important implications for robust toes, and long, sharp talons that are report- this and other such hypotheses. Along with show- edly stronger than those of any other African ing a strong preference by resident crowned hawk- eagle, they are voracious predators of small-to- eagles for cercopithecoids, skeletal analysis of the medium-sized mammals, and can kill animals as Ngogo kill aggregation reveals distinct patterns of large as bushbuck (ca. 30 kg) (Brown, 1971; Steyn, bone survival and damage. These findings indicate 1973; Daneel, 1979; Brown et al., 1982; Steyn, the feasibility of recognizing specific taphonomic 1983). They are significant predators of cercopithe- signatures of large raptors in fossil assemblages. coid monkeys throughout sub-Saharan Africa (Skorupa, 1989; Struhsaker and Leakey, 1990; Leland and Struhsaker, 1993, Maisels et al., 1993; Sample and methods Hart et al., 1996; Mitani et al., 2001), a fact attested to by the variety and intensity of mecha- The kill sample was collected between July 1996 nisms used by monkeys to deter predation by these and August 1999 from below the nests of two pairs raptors, including loud calls, tightened grouping of of crowned hawk-eagles. Details about nestlings troop members, rapid descent through the canopy, and fledglings associated with each nest are and aggressive defensive behavior (Gautier-Hion reported in Mitani et al. (2001). Searches at the and Tutin, 1988; Cordeiro, 1992; Maisels et al., first nest (Nest A) were conducted approximately 1993). once a week during nestling phases and periods of In this paper we provide a taphonomic inter- eaglet dependence, and at other times bi-weekly. pretation of prey assemblages accumulated by The second nest (Nest B) was discovered in June crowned hawk-eagles living in the Ngogo study 1999 and monitored bi-weekly over three months. area in Kibale National Park, Uganda and col- Searches involved comprehensive, diligent, and lected at their nests over a period of 37 months repetitive surface collecting. Material was not (Mitani et al., 2001). Eight diurnal anthropoid screened, but many small bones and bone frag- species are present at Ngogo and elsewhere in ments were collected. Because of the diligence of Kibale National Park, including a hominoid the searches for prey remains and collecting under (chimpanzees, Pan troglodytes), two colobines the nests, it is likely that the study sample accu- (black and white colobus, Colobus guereza, and red rately reflects the production of bone from the colobus, Piliocolobus badius), and five cerco- nests. pithecines (redtail monkeys, Cercopithecus ascan- The assemblages collected below the nests ius, blue monkeys, C. mitis, l’Hoest’s monkeys, comprised of bone, hair, boluses, eggshell, and C. lhoesti, olive baboons, Papio anubis, and grey- feathers. We collected a total of 387 skeletal speci- cheeked mangabeys, Lophocebus albigena) (Leland mens (NISP-number of individual specimens), in- and Struhsaker, 1987; Struhsaker and Leakey, cluding 345 specimens from Nest A and 42 1990; Mitani et al., 2000, 2001; Mitani and Watts, specimens from Nest B. Specimens include complete 2001). As primates, particularly cercopithecoids, and incomplete bones, as well as articulated sets of compose a large percentage of the mammalian bones. Where possible, the following attributes were biomass in the 12 km2 Ngogo area (Struhsaker, noted for each specimen: (1) identity of bone(s); (2) 1997), it is not surprising that monkeys dominate side; (3) taxon; (4) age-sex class; (5) dimensions; (6) the resident crowned hawk-eagle kill sample association; and (7) damage. Taxonomic assess- (Mitani et al., 2001). ments were made on the basis of pelage, size, and W.J. Sanders et al. / Journal of Human Evolution 44 (2003) 87–105 89 morphology of bones and teeth, in comparison relative abundance of a certain element i, Ni is with data from museum collections and published the observed number of a particular element (the sources. For example, colobine femora were sorted MNE value) in the taxon of interest, MNI is the from those of guenons and Lophocebus by differ- minimum number of individuals in the taxon of ences in size, degree of projection of the greater interest, and Ei is the number of skeletal element i trochanter, neck length, and intercondylar breadth expected in a complete skeleton (see Andrews, (see Nakatsukasa, 1994a,b, 1996). 1990; Lyman, 1994b). Ri values are expressed as a Age classes of adult, subadult, juvenile, and percentage representing bone survivability relative infant + neonate were based on size, degree of to what would be expected if all skeletons of all epiphyseal fusion, and tooth eruption. Postcrania individuals had been preserved. It is important to were assumed to be from adult animals if epiphy- point out, though, that because our MNI values ses were completely fused to diaphyses. In bones of were sometimes summed over different age and sex adult or nearly adult size, but where epiphyses classes, in many cases no Ri value approaches were cleanly missing or incompletely joined, indi- 100%. viduals were assigned to the preadult category. To investigate bone fragmentation, we looked Skulls were considered adult if all molars had at the percentage of each element that was whole erupted or if cranial sutures were closed. Skeletal (unfragmented). For each taxon of interest, we elements were sexed by size and robustness divided the number of whole bones of each (see Gautier-Hion, 1975). The soundness of these element by the NISP to arrive at a value, which we criteria was confirmed by observations in museum express as a percentage. One hundred percent collections of substantial dimorphism in dimen- means that the number of whole elements equals sions and extent of muscle markings, particularly